Synthesis and Crystal Structures of Two New Schiff Base Hydrazones Derived from Biphenyl-4-Carbohydrazide

Abstract  

The crystal structures of two novel Schiff base hydrazones have been determined by means of the X-ray diffraction. These compounds: N′-(E)-(2,5-dimethoxyphenyl)methylidene]biphenyl-4-carbohydrazide, C₂₂H₂₀N₂O₃ (1) and N′-(E)-(4-fluorophenyl)methylidene]biphenyl-4-carbohydrazide, C₂₀H₁₅FN₂O (2), are the first structurally characterized biphenyl derivatives of phenylmethylidene-carbohydrazide. Both compounds crystallize in the monoclinic space groups, 1 in P2₁/c space group with a = 13.987(2) ?, b = 16.426(3) ?, c = 8.214(2) ?, β = 98.12(2)°, and 2 in C2/c with a = 37.163(5) ?, b = 10.696(2) ?, c = 8.098(2) ?, β = 101.18(2)°. Both molecules have very similar bond lengths and angles pattern, even in the differently substituted phenyl ring. However, the conformations of the molecules differ significantly, the more crowded molecule 1 is much more folded than 2. The dihedral angle between the terminal ring planes is 56.17(6)° in 1 while in 2 it is as small as 2.83(14)°. In both structures relatively short and linear N–H···O hydrogen bonds (created by the best available hydrogen bond donor and acceptor) connect molecules into the chains along the unit cell parameter of ca. 8 ? in length. The next stage of the crystal architecture determination, the secondary interactions, are however quite different: in 1 there are almost solely dispersion van der Waals interactions while in 2 some more specific C–H···F and C–H···π interactions are also involved in the crystal packing.